The invention relates to a method and apparatus for controlling blowing air and/or cooling air in an I.S. glassware forming machine.
Control of blowing air during the production of hollow glass articles is significant for the rate of shaping and cooling and, associated with this, for the mechanical stability of the articles in the individual stages of the production process. In this case, it is a question of achieving a reproducible article quality in the face of external, but also internal, disruptive influences caused, e.g., by wear.
Patent document GB 2 297 548 A discloses a method and an apparatus for controlling the blowing pressure of a glassware forming machine, in which a line intended for supplying blowing air, a line intended for discharging blowing air and a line intended for measuring pressure issue in the blowing head which closes a blow mold at the top side. The lines used for the supply and discharge of blowing air are fitted with proportional valves which are connected to a computer-aided control device just like a pressure measuring device disposed at one end of the line used for measuring pressure. The intention is to achieve control of the pressure and the duration of the introduction of blowing air into the blow mold with the aim of producing in the blow mold a blowing and cooling effect which is adapted to the properties of the molten glass. In this case, consideration is to be given to the low mechanical stability due to the temperature of the produced hollow glass articles during and immediately after shaping, and to the low thermal conductivity of the glass. The control device forms a part of a control loop which acts upon the shaping process in the blow mold on the basis of the pressure measurement and optimum stored values, which can be changed where required, of other parameters by means of the proportional valves.
EP 1 894 894 A1 discloses a blow mold of an I.S. glassware forming machine, in which the blowing pressure is controlled with the condition that in a first phase only a relatively low pressure, which is sufficient to stabilize the hollow space of the parison, is developed in the latter, and in particular during the time of reheating, in which edge regions are reheated. This low pressure is such that still no shaping takes place. It is only in a second subsequent phase that blowing air, which is under high pressure, i.e., a pressure intended for actual shaping, is introduced into the said hollow space. Therefore, this document deals merely with the avoidance of deformations as a result of cooling air, which has entered into the blow mold, after reheating has been effected.
EP 1 318 111 B1 describes a method for controlling the blowing air pressure, in which stretching of the parison under the influence of reheating to the bottom of the blow mold is measured by a thermocouple and then, after an adjustable delay has lapsed, blowing air is introduced into the parison at a pressure sufficient to deform the parison to form the finished hollow glass article.
In the method disclosed in DE 601 10 139 T2, the pressure of the blowing air, to which a parison mold and a blow mold of an I.S. glassware forming machine are subjected during the shaping process, is determined in accordance with a stored time profile. For this purpose, proportional valves are disposed in the air supply lines to the parison mold and the blow mold and serve to provide a pressure progression which is characterized over time by stages, wherein a distinction is made between a blowing phase and a cooling phase.
Finally, it is known from document DE 601 08 548 T2 to effect control of the blowing air and the cooling air for the neck region of a hollow glass article in the blow mold of a glassware forming machine in each case with the cooperation of a solenoid valve which can be switched on and off and whose switching times are arranged in accordance with the operation cycle specified by a central controller, wherein the switching states of the valves and the input-side pressure of the blowing air and cooling air, as provided by the switching positions of said valves, upstream of the blow head are recorded and compared with the specified machine timing, and wherein in the case of deviations a trouble signal is generated.
The prior art listed above demonstrates that the actual object of the shaping process, the hollow glass articles to be produced, namely the state thereof, is taken into account at the utmost indirectly or only partially. The temperature of the article in its entirety is not measured in the individual stations of the process which, however, is of considerable importance for the deformation behavior and equally the mechanical stability of the article. The blowing air used for shaping both in the parison mold and in the blow mold always exerts not only a shaping effect but also a cooling effect and definitively determines the temperature to which the article is subjected. However, this temperature is subjected to numerous influences which are caused inter alia also by the environment. However, to achieve a reproducible product quality, it is necessary to produce uniform deformation conditions which is achieved only in partial aspects by this prior art.
In order to improve the quality of the hollow glass article and to accelerate the production time, it is known from document DE 10 2004 041 282 B1 to equip a blow head of a glassware forming machine with a blow pipe which can be lowered into the hollow glass article in a motor-driven manner, in this case by means of a piston-cylinder unit.